This invention relates to an improved process for converting coal or similar solid carbonaceous materials. More particularly, this invention relates to an improved process for liquefying coal and similar carbonaceous substances.
As is well known, coal has long been used as a fuel in many areas. For several reasons, such as handling problems, waste disposal problems, pollution problems and the like, coal has not been a particularly desirable fuel from the ultimate consumers point of view. Moreover, coal cannot be used directly, in areas where a liquid or gaseous fuel is required. As a result, oil and gas have enjoyed a dominant position, from the standpoint of fuel sources throughout the world.
As is also well known, proven petroleum and gas reserves are shrinking throughout the world and the need for alternate sources of energy is becoming more and more apparent. One such alternate source is, of course, coal since coal is an abundant fossil fuel in many countries throughout the world. Before coal will be widely accepted as a fuel, however, it is believed necessary to convert the same to a form which will not suffer from the several disadvantages alluded to previously and which will permit use in those areas where liquid or gaseous fuels are normally required.
To this end several processes wherein coal is either liquefied and/or gasified have been proposed heretofore. Of these, the processes wherein coal is liquefied appear to be more desirable since a broader range of products is produced and these products are more readily transported and stored.
Of the several liquefaction processes which have been heretofore proposed, those processes wherein coal is liquefied in the absence of added catalyst and in the presence of a solvent or diluent have been favored over catalytic processes even though the non-catalytic processes do not result in complete conversion of available carbon to either a liquid or gaseous product. One reason for this preference could be the relatively high cost of the catalyst and the cost associated with its recovery and recycle to the liquefaction. Another reason, however, could be that recycled catalyst tends to be rapidly poisoned and deactivated. In either case, the catalytic processes which have been proposed heretofore have not, on a continuous basis, approached stoichiometric conversion of the available carbon and have not been economically attractive when compared to the thermal conversion processes. Since stoichiometric conversion of available carbon would be most desired, however, the need for an improved catalytic process is believed to be readily apparent.